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2. Once the run cycle has terminated, the redundant
safety valve will close, the modulating valve will
return to its set position, and the draft inducer will
ramp up to its “ignition” setting for a 30 second
post - purge cycle
3. After the conclusion of the post-purge, the gas heat
control will enter the “OFF” state. All system
outputs are de-energized, but all safety devices are
still monitored.
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Once locked out on flame failure, the IC board will not
reactivate the ignition/combustion control circuit until it
is reset manually. To do this, press the reset button on
the front of the (IC) board case.
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e:: The modulating gas heaters are factory adjusted
for safe operation and to reach the nameplate
rated firing MBH for most areas of the country.
The proper air/gas ratio must be reached by the
service tech during start-up.
Electric Heat - Staged
When staged electric heat is configured in the unit, the
controller manages four binary outputs to provide up
to 6-stages of heat control; depending on size of the
electric heat installed. If four or less electric heat stages
are installed, the binary outputs are energized in
sequence to add additional heat capacity. If more than
four electric heat stages are configured, the binary
outputs are energized in combination to provide
increasing heating capacity with each stage.
Electric Heat - Modulating
Modulating Electric Heat provides improved control of
electric heat by modulating the first stage of heat.
When the first stage of heat reaches 100% capacity, the
next binary stage of electric heat is energized. The first
modulating stage of heat is reset to 0% capacity and
continues to modulate as heating capacity demand
increases.
An airflow limit control is applied when modulating
electric heat is configured to reduce the risk of high
temperature limit switch trips. This feature quickly
reduces modulating electric heat capacity when the
supply airflow decreases due to duct pressure control
or external supply fan control.
Electric Heat Protection
There are three automatic high temperature limit
switches that will trip when exposed to a high
temperature. They will reset automatically once the
temperature drops into an acceptable range. If any one
limit switch trips, all stages of heat are turned off. The
limits are mounted vertically on the heater terminal
plate and all three have the same temperature trip
point.
A manual reset temperature limit is also mounted near
the top of the terminal plate and serves as backup
protection. When exposed to high temperature, it will
turn all stages of heat off until the reset button is
manually reset. The electric heat protections operate
independently of the controller.
External Heat
The Symbio 800 controller supports external field
supplied heat sources. There is no factory wiring or
coordination between the controller and external heat.
When External Heat is configured, the supply fan
operates as required in heat modes and provides
ventilation defined by the mode.
Single Zone-VAV units have an External Heat Supply
Fan Speed Setpoint (adjustable) that defines the supply
fan speed in Occupied Heat modes of operation. The
supply fan operates at maximum speed for all other
heating modes. Continuous and cycling fan modes are
both supported.
Multi Zone-VAV units operate the supply fan under
duct static pressure control, unless commanded to go
to Maximum Heat.
Unoccupied Cooling
Unoccupied Cooling mode is used when the building is
unoccupied and the space conditions are exceeding
temperature limits. The unit is normally off in
unoccupied mode. If a valid space temperature input
rises above the Unoccupied Cooling Setpoint, unit
operation starts unoccupied cooling to manage space
temperature. The controller operates in Discharge Air
Control with ventilation disabled while DX or
economizer cooling capacity increases to satisfy the
Discharge Air Cooling Setpoint. Multi Zone VAV units
operate the supply fan with duct static pressure
control, other units operate the supply fan at maximum
speed. Cooling continues until space temperature is 4°
F less than the Unoccupied Cooling Setpoint, the unit
will then cycle off.
Unoccupied Cooling Mechanical Enable and
Unoccupied Cooling Economizing Enable are settings
to enable or disable cooling in unoccupied mode.
Unoccupied Heating
When the unit is in unoccupied mode and the valid
space temperature input falls below the Unoccupied
Heating Setpoint, unit operation starts unoccupied
heating to manage space temperature. The controller
operates in Discharge Air Control with ventilation
disabled while heating capacity increases to satisfy the
Discharge Air Heating Setpoint. The supply fan
operates according to heat type installed, see Heat
Types for more information. Heating continues until
space temperature is 4°F greater than the Unoccupied
Heating Setpoint, the unit will then cycle off.
Unoccupied Heating Enable is a setting to enable or
disable heating in unoccupied mode at the Front Panel.
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